1. Field of the Invention
The invention relates to a method and apparatus for recording the compression pressure of internal combustion engines, in which a stylus and a recording sheet are pressure-dependently moved relative to each other by a pressure-sensitive element, especially a Bourdon spring, and are brought into contact with each other during a part of the movement.
2. Prior Art
In a known method for recording the compression pressure, the stylus touching the recording sheet is pressure-dependently deflected during the compression process and thus draws a curve which ends at the maximum compression pressure attainable. To carry out this method, an apparatus is known which contains a Bourdon spring housed in a casing, which Bourdon spring can be connected, via a measuring line, with a spark plug aperture or an internal combustion engine, and a stylus is operatively connected with the Bourdon spring. In the casing, a support for the recording sheet is provided, the recording sheet and the support being stationary with respect to the casing. The stylus, which can be deflected by the Bourdon spring according to the pressure prevailing therein, is movable for the purpose of writing a line over the recording sheet. After the recording sheet has been clamped on the support, the stylus is made to rest on the recording sheet. When the stylus is subsequently deflected by the compression pressure, it writes the line on the recording sheet. Then the stylus is returned to its initial position by relief of the Bourdon spring.
Such known devices, generally called compression recorders, have hitherto been employed in two embodiments, namely, in one embodiment with a measuring range of about 2 to 12 kilopounds/square centimeter for Otto engines, and in another embodiment with a measuring range of about 10-40 kilopounds/square centimeter for Diesel engines. For testing the two engine types, it has been necessary to provide for two compression pressure recorders with different measuring ranges. Likewise, different recording sheets had to be employed for the two measuring ranges. This subdivision into two measuring ranges is necessary for reasons of recording accuracy. This is so because the friction of the stylus on the recording sheet during the compression process results, in connection with a single measuring range for both engine types, in an unacceptable recording incorrectness. With a measuring subdivision, this incorrectness can be reduced to 5%. This subdivision causes not only relatively large expenses when the compression pressure alternately of Diesel engines and Otto engines is to be recorded, but the recording itself is also more complicated since first of all the right compression recorder with the proper recording sheet must be provided